diff --git a/packages/web/src/App.svelte b/packages/web/src/App.svelte
index 2a0b7d8..8edc4f8 100644
--- a/packages/web/src/App.svelte
+++ b/packages/web/src/App.svelte
@@ -294,7 +294,15 @@
   /** pick-lock / master-key: prop the door for others once it opens. */
   let holdDoor = $state(false);
   /** mega-monster: which stat the chosen monster doubles. */
-  let megaBoost = $state<"life" | "movement">("life");
+  /** MEGA-MONSTER aimed at a monster: which of its two numbers to double. */
+  let megaPrompt = $state<{ instanceId: string; creatureId: string } | null>(null);
+  function castMega(boost: "life" | "movement") {
+    const m = megaPrompt;
+    if (!m) return;
+    megaPrompt = null;
+    dispatch(withMods({ type: "cast", instanceId: m.instanceId, target: { kind: "creature", creatureId: m.creatureId }, params: { boost } }));
+    clearSelection();
+  }
   /** teleport: the marked destination awaiting its confirming second tap. */
   let pendingTeleport = $state<{ x: number; y: number } | null>(null);
   /** Cards marked for discard. */
@@ -536,7 +544,6 @@
     tradeFrom = null;
     selectedCreature = null;
     selectedCard = null;
-    megaBoost = "life";
     holdDoor = false;
     pickChoice = false;
     pendingTeleport = null;
@@ -1054,11 +1061,16 @@
       clickCell(creature.position);
       return;
     }
+    if (selectedCard && selectedCard.cardId === "mega-monster") {
+      // "Doubles the existing life-points OR movement rate": the choice is
+      // asked, not defaulted — the cast waits on the answer.
+      megaPrompt = { instanceId: selectedCard.instanceId, creatureId };
+      return;
+    }
     if (selectedCard && (CREATURE_TARGET_CARDS.has(selectedCard.cardId) || cardDef(selectedCard.cardId).cardType === "attack")) {
       dispatch(withMods({
         type: "cast", instanceId: selectedCard.instanceId,
         target: { kind: "creature", creatureId },
-        ...(selectedCard.cardId === "mega-monster" ? { params: { boost: megaBoost } } : {}),
       }));
       clearSelection();
       return;
@@ -1681,6 +1693,27 @@
     {/if}
   {/if}
 
+  {#if megaPrompt && view}
+    {@const beast = view.creatures.find((c) => c.id === megaPrompt!.creatureId)}
+    <div class="scrim attack-scrim" role="alertdialog" aria-label="mega-monster">
+      <div class="attack-notice">
+        <div class="attack-title">Mega-Monster: the {beast ? cardDef(beast.kind).name : "monster"} grows</div>
+        <div class="attack-power">
+          "Doubles the existing life-points OR movement rate of any one monster." Which?
+          {#if beast}
+            Now {Number.isFinite(beast.maxDamage) ? `${beast.maxDamage - beast.damage} of ${beast.maxDamage} hits` : "unkillable"}
+            and {beast.movesPerTurn} move{beast.movesPerTurn === 1 ? "" : "s"} a turn.
+          {/if}
+        </div>
+        <div class="attack-actions">
+          <button class="stamp primary" onclick={() => castMega("life")}>Double its life-points</button>
+          <button class="stamp primary" onclick={() => castMega("movement")}>Double its movement</button>
+          <button class="hint-cancel" onclick={() => (megaPrompt = null)}>never mind</button>
+        </div>
+      </div>
+    </div>
+  {/if}
+
   {#if view?.pushPending && view.pushPending.pusheeId === view.you}
     <div class="scrim attack-scrim" role="alertdialog" aria-label="you are pushed">
       <div class="attack-notice">
@@ -2424,12 +2457,7 @@
                 {/if}
               {/if}
               {#if selectedCard?.cardId === "mega-monster"}
-                <span>— double its</span>
-                <button class="stamp tiny" class:lit={megaBoost === "life"}
-                  onclick={() => (megaBoost = "life")}>life-points</button>
-                <button class="stamp tiny" class:lit={megaBoost === "movement"}
-                  onclick={() => (megaBoost = "movement")}>movement</button>
-                <span>— then tap the monster</span>
+                <span>— tap the monster, then choose whether to double its life-points or its movement</span>
               {/if}
               {#if selectedCard?.cardId === "pick-lock" || selectedCard?.cardId === "master-key"}
                 <label class="inline"><input type="checkbox" bind:checked={holdDoor} /> hold the door open</label>